1. Field
This invention relates to blower and pump impellers having overlapping curved blades forming long, narrow, constant width flow channels. More particularly it pertains to a blower, which provides high flow characteristics while minimizing flow resistance. It is an impeller employing a plurality of discs having equally spaced spirally curved radial blades therebetween forming constant width and constant height flow channels, which produce a higher vacuum and pressure than previous designs. It is particularly suited for use in mineshaft and tunnel ventilation. It is also very useful where space is limited and a high volume of air is required through a small duct.
2. State of the Art
A number of blowers and impellers are known. Pauly, U.S. Pat. No. 5,741,123, hereinafter referred to as Pauly ""123, describes an impeller having constant cross section area along the length of the flow channels. The constant cross section is accomplished by reducing channel height in co-operation with an increasing blade spacing thereby providing a constant cross section area. Such a configuration causes the fluid being moved to flow with a twisting motion and is not optimum for keeping Reynolds"" number effects at minimum. That is, channel shape is a factor in generating turbulent flow. The present invention maintains a constant channel cross sectional shape, width, and height permitting the fluid to flow smoothly and laminar throughout the length of the flow channels. Conversely, Pauly ""123, FIG. 6, shows a multi-blade overlapping configuration of impeller. This configuration is described at Column 5 lines 16-32. Pauly ""123 makes no teaching about the blade shape or its span from the inlet end to the outlet end.
Eiichi Sugiura, U.S. Pat. No. 4,666,373, describes an overlapping blade impeller having constant blade height. Sugiura uses a blade of circular form and clearly teaches that the blades spacing narrows as it approaches the rim of the impeller. The present invention uses spiral blades and constant width flow channels. The Sugiura blades are segments of circles. Circular blades with any serious overlap will always converge at the impeller rim. Furthermore, Sugiura fails to teach how to determine adequate, proper, or optimum blade shape radii, or what is optimum spacing or overlap, nor how to select the circle about which the radii are arrayed. Because of the lack of design parameter teaching, it is impossible to conclude any minimum or maximum blade length and angular span as part of the Sugiura disclosure.
D. I. Doyle, U.S. Pat. No. 2,767,906, describes an overlapping blade impeller. Doyle also teaches that the spacing should narrow as the blade approaches the rim of the impeller. Moreover, Doyle (Column 5, lines 7-15) specifically states that the blades should not be parallel, nor should they diverge. The Doyle blades are segments of a spiral generated by an involute of a circle function not centered on the central axis of the impeller. Doyle specifically rejects involute blades developed around the impeller center as too long to be effective.
Pauly ""123 and Sugiura do not address minimizing Reynolds"" numbers and have nozzles pointing somewhat radially away from the tangent. Doyle minimizes the problem by having long sweeping flow channels (and blades), which inherently exit as near to tangential as practical. Doyle, Pauly ""123 FIG. 6, and others in their drawings show flow channels spanning an arc of well over 90 degrees. None teach about an optimum length or how to conclude that the lengths shown are near optimal.
There thus remains a need for an impeller invention, which optimizes both the channel length and tangential nozzle angle by teaching the optimum span for flow channels. The present invention with a blade having unusual curvature and spanning approximately 60 degrees with flow channels starting out as Archimedes spirals and then near the periphery the channels turn inward to exit more tangentially as it would if a longer channel was utilized provides such an invention.
It is an object of the present invention to devise a blower impeller having an optimal compromise within the various conflicting parameters affecting impeller performance.
It is another object of the present invention to devise a blower impeller that runs quietly.
It is another object of the present invention to devise a blower impeller blade lofting process that does not rely on generating tables using complex mathematical formula.
It is another object of the present invention to devise a blower impeller that may be manufactured without expensive specialized tooling or machinery.
It is another object of the present invention to devise a blower impeller that can be substituted for the original equipment impeller thereby improving the efficiency of installed blowers.
Unless distinguished by the context of usage, the following general definitions apply to these terms:
FLUID: includes gasses and liquids
AIR: unless determined otherwise by context, should be interpreted as a xe2x80x9cfluidxe2x80x9d
BLOWER: general usage of xe2x80x9cblowerxe2x80x9d is machinery for moving gasses, but in this context it should be interpreted as including pumps
PUMP: general usage of xe2x80x9cpumpxe2x80x9d in centrifugal machinery is for moving liquids, but here it should be interpreted as also pumping gasses.
LOFTING: a graphical process for developing shapes of products such as blades for blowers and pumps from which templates and other production tools are produced. Generally lofting is done at 1 to 1, full scale, but may be done on expanded or reduced scale.
SCROLL CASE: The collection chamber for gathering the outflow from an impeller and directing it into ducting or the like. Most scroll cases are formed in one of several known spiral shapes.
MOTOR: Any source of rotating power including, but not limited to electric, hydraulic, pneumatic motors, turbines, engines, and transmission systems between the power source and the impeller.
ARCHIMEDES SPIRAL, or SPIRAL OF ARCHIMEDES: A spiral that increases radius proportional to the angle turned. The formula for an Archimedes Spiral is R=K*(theta) in polar coordinates. Where R is the distance of the point from the center of generation. In this case, the center of the impeller disk, and theta is the angle turned from the polar origin (r=0, theta=0). It is therefore intended that the term xe2x80x9cArchimedes Spiralxe2x80x9d refers to blade shapes defined by the Archimedes Spiral formula, or other equivalent spiral formulae, where the spiral shape is defined by a plurality of curved or straight line segments approximated by the formulae.
The present invention comprises two parts:
First, it is directed to a blower impeller for installation within an operating housing. In most uses, the operating housing will have a lateral central housing air intake in communication with an interior circulation chamber containing the impeller, a peripheral air collection chamber, and a tangential exhaust. A drive shaft is journal mounted to the housing to extend within the circulation chamber and attached to the center of the impeller opposite the air intake. FIG. 6 illustrates the impeller installed in a common xe2x80x9csnailxe2x80x9d housing.
Second, it is directed to a method of lofting a specialized blade shape for production of impeller blades for the blower.
The present invention provides low turbulence flows with low Reynolds"" numbers. The enemies of efficient impeller design are turbulences associated with high Reynolds"" numbers, turbulences associate with exit streams crossing the flow in the collector scroll, surface drag (boundary effects) along the walls of the fluid flow channels, cavitation, entrance geometry at the inlet of the impeller flow channels, and inadequate inlet area in the impeller inlet eye. Reynolds"" number effects are controlled primarily by the narrowest dimensions of rectangular flow channels, the fluid velocity through the channels, and the viscosity of the fluid. Decreasing the spacing between blades improves the Reynolds"" number, but increases the interior surface area causing increased surface effect drag. All impeller blades forms have exit nozzles discharging the working fluid with a radial component of velocity. The radial component causes turbulence in the receiving plenum of the pump or blower case and should be held minimum consistent with the basic design of the impeller. To prevent the fluid exit stream from having significant radial velocity crossing the scroll flow, the flow channels should direct the exit stream as close to tangential as practical. This is primarily controlled by the direction of the exit nozzles, which point somewhat tangentially from the impeller rim. Surface drag is a function of flow velocity, but more importantly, of the total xe2x80x9cwettedxe2x80x9d area in the flow channels. The best control of wetted area is to keep the length of the flow channel as short as practical.
The low turbulence impeller of the invention comprises at least one disk for attaching a set of air-moving blades and attached to a shaft. The blades are uniquely shaped to define constant width spaces between adjacent blades extending from the collection chamber to the proximity of the rim of the attachment disk, and occupying an chord arc of 60 degrees.
A motor drives the shaft to turn the impeller and circulate the air through the blower. A typical motor utilized for air circulation will turn at about 3000 rpms to provide a high volume of air through a small duct. Thus configured with equidistantly spaced blades, the blower provides at least 20% greater efficiency than those where the blades are spaced apart wider at the outlet.
The impeller is attached to a shaft by any of many known methods. Small impellers often are attached by compression between a shoulder on the shaft end and a nut turned onto a threaded portion extending from the shoulder. Larger and heavier impellers may require an attachment hub and support ribbing.
In the simplest embodiment, there is only one disk to which the blades and shaft are attached. The housing itself serves as the cover of the fluid channels A second parallel circular disc may be attached to the blades opposite the attachment disk to form a closed impeller. The second impeller disk has a central air intake opening aligned with and in communication with the housing fluid inlet.
In another preferred embodiment, the impeller is constructed of more than two parallel circular discs with central air inlets having similar shaped blades affixed there between.
In a preferred embodiment for use in tunnels, mines, and lumber mills, the discs and blades are spaced sufficiently apart to prevent debris picked up in the intake air from obstructing the flow channels. This spacing is particularly important where very large blowers with high velocity airflows are employed. Preferably, the angle of curvature of the blades at the gas inlets is also selected to allow the air entering the impeller to be at approximately the same angle as the curve of the blades to minimize inlet losses. In addition, the flow channels have the same cross-section area throughout their length to prevent turbulence in the air flows passing through and out the blade air outlets.
The preferred impeller blade design has the blades of the impeller curved on a cord of sixty degrees. This allows for maintaining the distance between the blades at a constant distance from the center of the impeller to the outside edge, thereby maintaining the pressure while reducing the turbulence of the air. This is accomplished by dividing the circumference of the outer circular impeller blade drive base into 10 degree radii. Five equidistant concentric circles are then drawn with diminishing radii to serve as layout guides. The fifth inner circle locates the inner end and the outer circle locates the outer end of the blades to be drawn. The first curved blade segment shape is then drawn by connecting a series of intersection points of the 10 degree radii with the inner, outer and four equidistant intervening concentric circles with a French curve. The first point is the outer circle intersect at the 60 degree segment. The second point is the fourth inner concentric circle intersect with the 50 degree segment. The third point is the third inner concentric circle intersect with a 30 degree segment. The fourth point is the second inner concentric circle intersect with the 20 degree segment. The fifth point is the first inner concentric circle intersect with the 10 degree segment. The sixth point is the inner circle intersect at the 0 degree radius. These six points form the extended radial edge of the outside edge of the impeller blade proximate the air inlet, which gradually changes in curvature toward the outside edge of the impeller blade proximate the air outlet. The next circular blade is then drawn parallel to the first blade starting from the width of the inner blade opening between the adjacent blade, and ending 60 degrees from its extended radius of the edge of the next inner blade.
The layout method is straightforward and independent of the tools. It uses either manual methods of drafting or equivalent automated methods employing computer software, such as AUTO CAD where many blades are employed. Although automated methods are much faster and provide more detailed drawings, the layout method does not require extensive calculations and the plotting of long tables of data points. It also can be accomplished with or without the actual formulae plots.
The impeller may be made using welded, machined, riveted, or spot construction. The choice employed would be determined by the thickness of the material used and the purpose of the blower. For example, a blower used for ventilation could have the blades spaced closer together if air carried debris is not a factor. If debris is a factor, it may be necessary to get in between the blades for clean out. Pop rivets may be employed for this purpose to easily separate and reassemble the components. In other embodiments, the components may be preformed as single pieces assembled by injection molding. Where weight is a factor, a titanium or aluminum type of slug with a center inlet air opening and slots for the cover machined to specification. A computerized milling machine is then programmed to cut a cord of 60 degrees between each blade to form one piece construction with the back of the impeller laid flat on the milling machine. The impeller cover, if used, is then assembled onto the impeller.
Preferably, the tangential exhaust of a housing is structured for coupling with a hose or conduit to transmit the blower air flows. In larger embodiments, the tangential exhaust couples directly with large ducting to deliver the air flows.
The blower invention thus provides a new highly efficient blower configuration, which directs high volumes of air into a given space.